1. Field of the Invention
This invention relates to an apparatus for measuring the refractive power of an optical system, such apparatus being utilizable as an eye-refractometer device, an automatic lens meter or the like.
2. Description of the Prior Art
An example of the eye-refractometer device will hereinafter be described.
Generally, in the measurement of the refractive power of an eye, it is necessary to measure the astigmatism main diametral line direction and the refractive power in that direction. Apparatus for effecting such measurement on the basis of the principle of the skiascopy are already known. The skiascopy is a method wherein when a slit-like light beam is moved in the pupil of an eye to be examined, the movement of the reflected light from the fundus of the eye is observed and a so-called neutral condition in which light does not move is caused to appear, whereby the refractive power of the eye to be examined is measured. To cause such neutral condition to appear, there is a method wherein lenses having various refractive powers are disposed immediately before the eye to be examined and the eye is observed from a predetermined position, so that the refractive power of the eye is obtained by a lens which brings about the neutral condition, and a method wherein the eye is observed with the observation distance being changed and the refractive power of the eye is obtained from a distance which provides the neutral condition. As an apparatus for photoelectrically measuring the refractive power of an eye by the skiascopy, an apparatus using the former method is disclosed in U.S. Pat. No. 3,136,839 and an apparatus using the latter method is disclosed in U.S. Pat. No. 3,715,166. In these measuring apparatus, the entire apparatus is rotated to detect the astigmatism axis direction of an eye to be examined and an accurate servo mechanism for making the entire apparatus exactly coincident with the main diametral line direction is indispensable. This has led to complexity and bulkiness of the apparatus and has been disadvantageous for quick measurement.
To overcome such disadvantages, a method of knowing the refractive power of an eye from the speed and direction of movement of the reflected light from the fundus of the eye is known, for example, from Japanese Laid-open Patent Application No. 160538/1980 (corresponding U.S. application Ser. No. 152,602 now U.S. Pat. No. 4,353,625). That is, an eye-refractometer using this method has a beam splitter; a projection optical system disposed in one optical path of said beam splitter to project a beam of light into the pupil of an eye to be examined therethrough and to effect scanning linearly thereof; a condensing optical system including a condenser lens fixedly provided in the other optical path of said beam splitter; a diaphragm member fixedly provided behind said condenser lens and a light receiving member fixedly provided further behind said diaphragm member at a conjugate point with the cornea of said eye relative to said condenser lens, said condensing optical system being disposed to condense the reflected light from the fundus of said eye on said light receiving member through said beam splitter; a beam rotating member disposed at the eye side of said beam splitter to rotate the beam about the center of the optical path as its rotational axis; and a signal processing system for processing the signals coming from said light receiving member. However, this device requires an image rotating prism for rotating the light beam to detect the main diametral line direction of astigmatism, but it is considerably difficult in manufacture and adjustment and time-consuming to rotate such image rotating prism about the optical axis without any error.
In view of the fact that an eye can be regarded as an optical system, it is a matter of course that the eye-refractometer as described above can be used as an apparatus for measuring the refractive power of an optical system such as a spectacle lens, without being changed in principle, and in that case, of course, the foregoing discussion likewise holds true.